Microphone array systems are known and they enable spatial selectivity in the acquisition of acoustic signals, based on using principles of sound propagation and using signal processing techniques.
Table-top microphones are commonly used to acquire sounds such as speech from a group of users (speakers) seated around a table and having a conversation. The quality of the acquired sound with the microphone is adversely affected by sound propagation losses from the users to the microphone.
One way to reduce the losses in sound propagation is to use a microphone array system. The microphone array system includes, broadly, a plurality of microphone transducers that are arranged in a selected spatial arrangement relative to each other. The system also includes a microphone array interface for converting the microphone output signals into a different form suitable for processing by the computer. The system also includes a computing device such as a computer that receives and processes the microphone transducer output signals and a computer program that includes computer readable instructions, which when executed processes the microphone output signals. The computer, the computer readable instructions when executed, and the microphone array interface form structural and functional modules for the microphone array system.
Beamforming is a data processing technique used for processing the microphone transducers' output signals by the computer to favour sound reception from selected locations in a reception space around the microphone array. Beamforming techniques may be broadly classified as either data-independent (fixed) or data-dependent (adaptive) techniques.
Apart from sound acquisition enhancement from selected sound source locations in a reception space, a further advantage of microphone array systems is the ability to locate and track prominent sound sources in the reception space. Two common techniques of sound source location are known as the time difference of arrival (TDOA) method and the steered response power (SRP) method, and they can be used either alone or in combination.
Applicant believes that the development of prior microphone array systems for speech acquisition has mostly focused on applications for acquiring sound from a single user. Consequently microphone arrays in the form of linear or planar array geometries have been employed.
In scenarios having multiple sound sources, such as when a group of speakers are engaged in conversation, e.g. around a table, the sound source location or active speaker position in relation to the microphone array changes. In addition more than one speaker may speak at a given time, producing a significant amount of simultaneous speech from different speakers. In such an environment, the effective acquisition of sound requires beamforming to multiple locations in the reception space around the microphone array. This requires fast processing techniques to enable the sound source location and the beamforming techniques to reduce the risks of sound acquisition losses from any one of the potential sound sources.
Also, linear microphone array geometries that are known include limitations associated with the symmetry of their directivity patterns obtained from the microphone array. The problem of beam pattern symmetry is alleviated using microphone arrays having planar geometries. However its maximum directivity lies in its plane which limits its directivity in relation to sound source locations falling outside the plane. Such locations would for example be speakers seated around a table having their mouths elevated relative to the array plane.
Clearly therefore it would be advantageous if a contrivance or a method could be devised to at least ameliorate some of the shortcomings of prior microphone array systems as described above.